Weight affects survival of primary total knee arthroplasty: study based on the Danish Knee Arthroplasty Register with 67,810 patients and a median follow-up time of 5 years.

Background and purpose - Obesity is a rising issue worldwide and growing evidence supports poor outcome amongst obese patients following total knee arthroplasty (TKA). Using nationwide registries we investigated the association between bodyweight and risk of revision of primary TKA. Patients and methods - All primary TKA performed during 1997-2015, weight at time of primary TKA and subsequent TKA revisions were identified in the Danish Knee Arthroplasty Register (DKR). Data on comorbidities and a priori selected confounding variables were collected from nationwide registries. The association between weight and 1st time TKA revision was calculated as both crude and adjusted hazard ratios (aHR) with 95% confidence intervals (CI) using Cox regression. Results - Of 67,810 identified primary TKAs, 4.8% were revised within a median follow-up time of 5.4 years. No association between weight and risk of any revision in patients aged 18-54 and 55-70 years was found. Increased risk of any revision was seen in patients >70 years, 80-89 kg (aHR =1.5, CI 1.2-1.8), 90-99 kg (aHR =1.7, CI 1.3-2.1) and patients >99 kg (aHR =1.6, CI 1.3-2.1), as well as those weighing 45-60 kg (aHR =1.4, CI 1.1-1.9) compared with same aged patients weighing 70-79 kg. Interpretation - We found a complex association between weight and knee arthroplasty survival. There was an increased risk of any revision in patients older than 70 years of age weighing <60 kg and >80 kg. Patients aged 18-55 years weighing 60-69 kg had a lower risk of revision compared with all other weight groups, whereas weight was not found to affect risk of any revision in patients aged 55-70 years.